Rotor for axial flow air compressor



Aug. 16, 1955 w. A. LEDWITH ROTOR FOR AXIAL FLOW AIR COMPRESSOR Filed Nov. 28, 1949 2 Sheets-Sheet 1 N V EN TOR.

I NHL-TEE 19. L ED W/ TH w. A. LEDWITH 2,715,494

ROTOR FOR AXIAL FLOW AIR COMPRESSOR Aug. 16, 1955 2 Sheets-Sheet 2 Filed Nov. 28. 1949 INVENTOR. WJLTIE ,9. dZPV/Tl/ BY I United States Patent Ofilice 2,715,494 ?atented Aug. 16, 1955 ROTOR FOR AXIAL FLOW AIR COMPRESSOR Walter A. Ledwith, Glastonbury, Conn., assignor to the United States of America as represented by the Secretary of the Air Force Application November 28, 1949, Serial No. 129,831

1 Claim. (Cl. 230134) The present invention relates to an axial flow air compressor of reduced overall length and improved structural arrangement of the elements making up the compressor rotor assembly.

The primary object of the invention is to provide an axial flow air compressor especially for use in a turbojet aircraft engine and having central supporting members or end bells extending within a multiple wheel rotor assembly for rigid attachment thereto, whereby the overall length of the rotor and end bell assembly may be reduced to a minimum.

A further object of the invention is to provide an axial flow air compressor including a multiple wheel rotor in which the successive wheels are held together by a plurality of longitudinally extending draw bolts and in which the rotor is supported for rotation on a central axis by means of oppositely extending end bells each having a pcripheral flange interposed between adjacent rotor wheels near but spaced from the opposite ends of the rotor.

Another object of the invention is to provide a rotor assembly for an axial flow air compressor in which the rotor assembly includes a number of rotor wheels assembled into a rigid unit and in which each end of the unit is rotatably mounted by means of a member rigidly connected to the rotor assembly and having an axle-like projection integrally joined to a cone-shaped web or flange attached to the rotor assembly at its outer periphery, whereby the rotor supporting means will possess a maximum of axial and radial rigidity.

Another object of the invention is to provide a multiwheel rotor for an axial flow air compressor in which the rotatably mounted supporting means for the rotor is telescoped within the rotor wheel assembly to reduce the overall length of the rotor and air compressor.

Another object of the invention is to provide a stronger as well as simpler supporting means for a multi-wheel rotor as found on axial flow air compressors.

The above and other objects of the invention will become apparent upon reading the following detailed description in conjunction with the accompanying drawing, in which:

Fig. l is a longitudinal cross section of the forward end of a turbojet aircraft engine showing the principal features of construction of the present axial flow air compressor.

Fig. 2 is a transverse cross sectional view of the rotor assembly taken between one end bell member and the contiguous rotor wheel.

Fig. 3 is a large scale sectional view of the joint between flanges 8b, 8c and the axially extending wheel flange.

In aircraft engines of the turbojet type including an axial flow air compressor the frontal area of the engine is reduced to a minimum but the overall length is usually at a maximum because the engine includes in end-to-end series starting at the front: an accessory section, an air compressor, a set of combination chambers, a gas turbine and an exhaust section leading into the free atmosphere or perhaps into an extended tail pipe. Thus it is clear that if any one of these units can be reduced in length the overall engine length can be reduced accordingly. In accordance with the principles of the present invention a substantial length reduction can be accomplished in the axial flow compressor, as found on many modern turbojet engines, by a telescopic arrangement of the end members or bells with respect to the multi-wheel rotor assembly. The end bells, which are axially extended to form oppositely extending axles or shafts for rotatably mounting the rotor, are mounted at their peripheral edges between adjacent rotor wheels instead of being attached to opposite ends of the completely assembled rotor assembly. These end bell and bearing elements are coneshaped throughout a substantial portion of their axial length and thus have considerable axial as well as radial rigidity, to prevent any tendency toward vibration due to rapidly rotating unbalanced loads. Thus the vibration and balancing problems in the compressor will be less serious with the present advanced construction.

Considering the illustrated embodiment of the invention, attention is directed to Fig. 1 in which the forward end and compressor section of a turbojet engine is illustrated in vertical longitudinal cross section. The engine casing 1 is made up of flanged sections joined together in end-to-end relation in any suitable manner. The outwardly flared front casing section 2 forms the outer wall of an annular air inlet 3 receiving ram-compressed air from the free atmosphere. The inner wall of the air inlet is provided by a cylindrical casing 4 extending rearwardly only as far as the axial flow compressor and serving to support an accessory section housed within the domelike cover member 5. The rear edges or marginal portions of cover member 5 are detachably secured to the casing 4 in any desired manner. Also the inner casing 4 supports an inwardly directed bearing member 6 within which is mounted an antifriction bearing assembly 7 to rotatably support the axle-like portion 8a of the end hell 8. An air seal 9 of any suitable design is secured to the inner portion of bearing member 6 to prevent loss of compressed air through the accessory section of the engine by way of the antifriction bearing assembly 7. Supported by the outer and inner casings 1 and 4 is the first row 10 of stationary compressor blades forming air inlet guide vanes to direct the ram-compressed air onto the first row of rotor blades to best advantage. The first row of stator blades form what may be called the air inlet diaphragm and in accordance with usual practice these blades are protected against foreign objects by an annular impact screen (not shown).

As will be seen in Figs. 1 and 3 the end bell8 extends rearwardly from the axle portion 8a and has a conical or flared base portion 30 integrally joined at its outer periphery to a forwardly and axially extending annular flange 8b positioned in overlapping relation to the cylindrical flange 31 on adjacent rotor wheel 17 and which is in turn integrally joined to a narrow radial annular flange 8c forming part of the rotor. Flange 8c is disposed between confronting cylindrical flanges 31 of two adjacent rotor wheels at the forward end of the rotor and includes axially extending uniformly and circumferentially disposed draw bolt receiving bores, see Fig. 2. The axle portion 8a extends forwardly for rotatable support in the bearing 7 and forwardly of the bearing it extends into the accessory section covered by the hollow cap or dome 5 for driving various accessories and auxiliaries and for connection with an engine starter also enclosed within the cap 5. At the rearward end of the rotor assembly is another end bell 12 including an integral axle extension 1202 joined to a conical or flared portion extending forwardly and outwardly from the axle extension. The conical base portion 30 is integrally joined at its outer periphery to a rearwardly extending end of the rotor, and includes axially extending, uni-,

formly and circumferentially disposed draw bolt receiving bores forming part of the rotor to be clamped in assembled relation by the draw-bolts 11. The axle 12a is rotatably supported by an antifriction bearing 13 and extends rearwardly to a shaft coupling means secured to the main shaft of the engine, which is driven by the turbine unit of the engine. The bearing assembly 13 is mounted on the central axis of the engine by means of a bearing flange 14 supported from the engine casing 1 by means of an annular row of radial guide vanes 15.

The supporting means for the rotor assembly has been described in some detail above since this is the principal feature of the invention. Besides resulting in a reduced overall length and a more compact structure, the end bells 8 and 12 also have end projectons which serve as axle or trunnion members and thus eliminate a central shaft clear through the rotor assembly. The remainder of the rotor assembly comprises alternate rotor wheels 19 and spacer links 18. Each rotor wheel includes a central disk-shaped portion open at the center to decrease the weight without sacrificing rigidity and strength, and has a cylindrical axially extending flange portion 31 secured to the periphery of the central disk-shaped portion extending toward the flange portion of adjacent rotor wheels. Each cylindrical flange is provided with uniformly and circumferentially spaced ax ally extending bores adapted to receive securing draw bolts. The flange 31 on the first rotor wheel 16 abuts one side of radial flange 8c and the I flange 31 on the second rotor wheel 17 abuts the other side, see Fig. 1. Both end bells are arranged similarly i 6 as may be seen in Fig. l and the whole assembly is rigidly secured together by the draw-bolts 11 having nuts 11 on their opposite ends. The complete rotor assembly is more or less cylindrical in shape with the various rotor wheels and blades projecting from the outer cylindrical surface thereof.

The sections making up the outer engine casing I carry rows of fixed compressor blades 21 situated between moving blades on the rotor wheels. As may be seen in Fig 1 the compressor blades are progressively shorter in succeeding rows starting at the forward end of the engine and extending rearwardly, since the progressive compression of the air results in a smaller volume after each stage is passed. The air after being fully compressed passes between the guide vane and thence into the engine combustion chambers (not shown). While the compressor as described is particularly intended for use on aircraft gas turbine power plants, it should be understood that it is also adapted for general use wherever an axial flow air compressor may be required. While the annular attaching flanges 8c and 120 of the end bells 8 and 12 are shown as interposed between cylindrical flanges of the first two and last two rotor wheels respectively, it should be emphasized that the bell flanges may be positioned between other adjacent rotor wheels especially on multi-stage compressors having more stagesthan the illustrated compressor.

The embodiment of the invention herein shown and described is to be regarded as illustrative only and it is to be understood that the invention is susceptible of variations, modifications and changes within the scope of the appended claims.

I claim:

In an axial flow air compressor, a compressor rotor assembly comprising a series of parallel axially spaced rotor Wheels, each wheel comprising a central disk-shaped portion open in the center and having a cylindrical axially extending flange portion projecting from each side and secured to the periphery of said disk-shaped portion, and extending toward cylindrical flange portions or. adjacent rotor wheels, each cylindrical flange being provided with uniformly and circumferentially spaced axially extending draw bolt receiving bores, a pair of end bells adjacent opposite ends of the rotor, each end bell having a frustoconical portion with said portions integrally connected at their apical ends to axially extending shaft portions projecting away from each otherat opposite ends of the rotor, each end bell including an axially extending an: nular flange at the base of the frusto-conical portion extending away from said base end toward the apical end in overlapping relation with one of said cylindrical flange portions of the adjacent rotor wheel, the base of said conical portions abutting against the disk-shaped portions of said adjacent rotor wheels, each end bell further including an annular outwardly extending radial flange integrally connected to said axially extending flange at the edge remote from the frusto-conical base of the end bell, the annuar radial flange of one bell being located between confronting cylindrical flanges of two adjacent rotor wheels at one end of the rotor, and the annular radial flange of the other bell disposed between confronting cylindrical flanges of-the two adjacent rotor wheels at the opposite end of the rotor, each annular radial flange including axially extending uniformly and circumferentially disposed draw bolt receiving bores, draw bolts extending through the bores in the cylindrical flanges in the rotor Wheels and the annular radial flanges of the two end bells, means on the opposite ends of the drawbolts to fasten said cylindrical'flanges tightly together to keep the assembly of said compressor rotor as a rigid structure.

References Cited in the file of this patent UNITED STATES PATENTS 1,221,087 Parsons et al Apr. 3, 1917 2,410,769 Baumann Nov. 5, 1946 2,427,614 Meier Sept. 16, 1947 2,520,697 Smith Aug. 29, 1950 2,575,237 Sollinger 1 Nov. 13, 1951 2,628,766 Rydmark Feb. 17, 1953 2,639,885 Ledwith May 26,1953 FOREIGN PATENTS r 586,200 Great Britain Mar. 11, 1947 

